Refrigeration evaporator coil

ABSTRACT

Air refrigeration equipment having in addition to the normal evaporator air inlet area a second air inlet area separated from the first area by a restrictive opening so that when the first air inlet area is blocked by frost, the air will go through the restrictive opening and into the evaporator through the second air inlet area. Located adjacent to the second air inlet area and on the opposite side thereof from the restrictive opening is a frost collecting cavity. The restriction between the first and second inlet areas is so arranged that the frost which is airborne as it passes through the restriction is carried by inertia forces into the frost collecting cavity. This invention permits an increase in the time period between defrost cycles in air refrigeration apparatus.

United States Patent Steelman 1 Aug. 12, 1975 [731 Assignee: Clark Equipment Company,

Buchanan, Mich.

221 Filed: May 17,1974

21 Appl. No.: 470,762

[52] US. Cl. 62/272; 62/255; 62/256;

' 62/80 [51] Int. Cl. F25D 21/00 [58] Field of Search 62/71, 80, 272, 317, 150, 62/151, 255, 256

[56] References Cited UNITED STATES PATENTS 2,810,267 10/1957 Reuter 62/256 3,012,413 12/1961 Anderson 62/272 3,364,696 l/l968 Maxwell 1. 62/414 3,638,449 2/1972 Lichtenberger 62/272 Primary Examiner-Wil1iam .1. Wye Attorney, Agent, or Firml-larry G. 'I'hibault [5 7 ABSTRACT Air refrigeration equipment having in addition to the normal evaporator air inlet area a second air inlet area separated from the first area by a restrictive opening so that when the first air inlet area is blocked by frost, the air will go through the restrictive opening and into the evaporator through the second air inlet area. Located adjacent to the second air inlet area and on the opposite side thereof from the restrictive opening is a frost collecting cavity. The restriction between the first and second inlet areas is so arranged that the frost which is airborne as it passes through the restriction is carried by inertia forces into the frost collecting cavity. This invention permits an increase in the time period between defrost cycles in air refrigeration apparatus.

BACKGROUND OF THE INVENTION Air cooling coils in refrigeration equipment are normally held at a temperature below the frost point of the incoming air. As the result, frost builds up on the coils particularly in the region where the air impinges on the coils at the air inlet area. This frost build-up at the air inlet is quite rapid when the moisture content of the incoming air is high. As the frost builds up, the passage of air through the air inlet area is restricted sufficiently to make the air cooling coils ineffective. This problem is quite serious in the case of evaporator coils of open display cases of the type used in retail merchandizing refrigerated foods. The coils and the fins on the coils used to cool the air become rapidly coated with frost to such a thickness as to prevent air flow through the evaporator. When this happens, the air ceases to circulate and it is necessary to defrost the evaporator. During the defrost cycle, the air is not properly cooled. It is usual practice to inject heat energy into the coils during the defrost cycle and this increases the cost of operating the air refrigeration system. It is therefore desirable that the cooling period between the defrost cycles be as long as possible in order to minimize the number of expensive defrost cycles.

PRIOR ART The problem of frost build-up at the inlet area of an evaporator is not new and many attempts have been made to minimize the adverse effects of this frost build- One attempted solution has been to provide a multiplicity of air inlets and/or outlets spaced along the length of the air cooling coils so as to distribute the frost build-up along the length of the coil and thus lengthen the time between defrost cycles. This approach to the solution of the problem is illustrated in the following US. patents:

US. Pat. No. 2,152,291 Star et al.

U.S. Pat. No. 2,495,626 Booth US. Pat. No. 3,364,696 Maxwell A second approach to minimizing the difficulties resultingfrom reduced air flow due to frost build-up has I been to so design the coil and fin configuration of the evaporator coil to minimize the effect on air flow of frost build-up and thus increase the time between defrost periods. This approach to the solution of the problem is illustrated in;

US. Pat. No. 3,359,750 Hanson.

In certain of these patents, the bypass opening is located in the refrigerated space and this creates a change in the air temperatures and air circulation as the frost builds up on the inlet area of the refrigeration coils.

SUMMARY OF THE INVENTION The present invention relates to apparatus permitting an increase in the cooling period between defrost cycles in refrigeration systems. Particularly it relates to air cooling means having a primary air inlet area that is subject to stoppage of air movement by frost buildup and providing such a cooling means with a second inlet area that becomes effective on stoppage of the first inlet area. The invention contains provision for a restricted air passage through which air passes when the first inlet area is closed by frost into a plenum chamber and from the plenum chamber through the second inlet air area. The plenum chamber also has a frost collecting cavity into which airborne frost is propelled.

The invention also relates to air cooling apparatus for food refrigerated display cabinets in which the air flow through the cabinet is subjected to only minimal disturbance as the result of frost build-up on the air cooling coils and one which permits a maximum cooling period between defrost cycles.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an air cooling apparatus having a maximum cooling time period between defrost cycles.

It is another object of the present invention to provide an apparatus in which the air cooling means has primary and secondary air inlet areas with a restrictive passge there between so that the preponderance of air passes through the primary air inlet area until it is obstructed by frost after which the cooling cycle continues with the air passing through the secondary inlet area.

It is another object of the present invention to provide an air cooling apparatus having a restrictive air bypass between a primary and secondary air inlet to permit a longc oolingcycle between defrost cycles and one. causinga minimaldi's'turbance ofair in' the space being pended claims.

BRIEF DESCRIPTION OF THE DRAWINGS The FIGURE in the drawing represents a cross section of a refrigerated food display case 2 having a refrigerated area in which food items 6 supported by a support shelf 12 are displayed. 13 may be glass sliding doors or other conventional access means to the refrigerated display area. Air from the display area 4 is exhausted through the passages 14 and 15 around the support 12 and then passes through cooling coils 16 and up the passage 8 through the air discharge grille 10 to complete circuit into the refrigerated area 4-.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION Referring now specifically to the drawing and to details of the preferred embodiment of the present invention, 2 is a refrigerated display case of the type normally used in retail food stores for the display of refrigerated or frozen meat and other foodstuff. The case as illustrated has sliding glass doors 13 for access to the refrigerated space 4. The meat or foodstuff 6 is placed on a support 12 which may be of either solid or perforated material. Air is exhausted from the refrigerated space 4 through passages 14 and I5 surrounding the support 12 into a plenum chamber 18. Air propulsion means 20 here shown as an electric fan is used to move the air from the plenum chamber 18 into the air conducting conduit 22 by maintaining the air pressure in the conduit 22 above the pressure in the plenum chamber 18. The air cooling means 16 is here shown as an evaporator coil having a vertical dimension of approximately 4 inches and a dimension from front to back of approximately 16 inches with the dimension of the case depending on the size of the case. If the case is a standard 54 inchcase,'the evaporator 16 will be approximately 48 inches long. The primary or first air inlet area 24 is therefore approximately 4 inches high as is the air outlet area 26. The second inlet area 28 is 12 inches from front to back and therefore has approximately 3 times the area of the primary inlet area 24. The restrictive bypass 30 between the first and second inlet area in the preferred embodiment is /2 inch and runs the length of the evaporator coil 16 and therefore has approximately /s the area of the first air inlet area 24 or 1/24 the area of the second inlet area 28. The restriction 30 lies in the same plane as the first inlet area 24 so that the air coming through this /2 inch slot travels across the surface of the second inlet area 28 toward the frost collecting cavity 32. This frost collecting cavity is approximately 3 inches deep and runs the length of the air cooling means 16. The plenum chamber 34 is approximately 3 inches high and runs the length of the air cooling means or evaporator 16. The air cooling means 16 having a dimension of 4 inches by 16 inches by approximately 48 inches and is of standard design OPERATION OF THE PREFERRED EMBODIMENT OF THE INVENTION Referring tothe FIGURE, the operation of the present invention is as follows. Air is exhausted from the chamber 18 by means of the air propulsion means 20 .here shown asan electric fan into an air conditioning conduit 22 which includes an air cooling means 16. After the defrosting cycle when the air cooling means '16 here shown as an evaporator is fully clear of frost, air enters the first air inlet area 24 and passes through the air cooling means 16 and out the air outlet 26 at a lower temperature than that at which it entered. The air then passes up the conduit 8 through the diffuser back through the refrigerated area 4 into the plenum chamber 18 where the air circulation cycle is repeated.

As frost builds up on the first air inlet area 24, pressure' is built up in the plenum chamber 36 and as this pressure builds up an increasing volume of the circulated air passes through the restrictive opening 30 which has approximately Vs the cross section area of the first inlet area 24. As this frost builds up on the air inlet area 24, it'becomes plugged and the ent-Ire circulated volume of the air passes through the /2 inch air restriction 30'into a second plenum chamber 34. The velocity of the air through the restriction 30 is sufficient when the air inlet area 24 is plugged to cause airborne frost to be thrown across the second inlet area 28 into the frost collecting cavity 32 as the air makes a 90 turn and enters the air cooling means 16 through the second inlet area 28. The cross section area of this inlet 28 is approximately 3 times the cross section area of the air inlet 24 and this together with the inertial separation of the frost particles from the air and collection in the cavity 32 results in only a very slow buildup of frost on the coils and fins in the air inlet area 28. The air coming through the air inlet 28 is cooled by the air cooling means 16 and exhausted through the air outlet area 26 and afterwards proceeds up the air conduit 28 and through the plenum chamber 9 and diffuser 10 into the refrigerated area 4 and thence to the plenum chamber 18 where the air circulation cycle begins anew.

Except for the bypass of air through the air inlet area 28 as permitted by the restriction 30, the refrigeration cycle becomes inoperative as soon as the air inlet area 24 is plugged with frost. This bypass 30 permits the air to enter a second air inlet area 28 into the air cooling means and thus, extends the effective cooling period severalfold. This extension of the cooling period is lengthened even a greater amount by the inertial rejection of the frost particles from the air stream into the frost collecting cavity 32 so that this airborne frost is no longer available to plug the second air inlet area 28.

It may thus been seen that by the use of the present invention, the 'period between the defrost cycles is lengthened severalfold without appreciably lengthening the time period of the defrost cycle. By the use of this invention, cool air is permitted to flow over the refrigerated material in the display case for longer periods of time, thus minimizing the deterioration of the quality of the foodstuff displayed in the case 2.

Having thus described the preferred embodiment of the present invention, it will, of course, be obvious that various changes may be made in the form, details and proportions of parts without departing from the scope of the invention which consists of the matter shown and described herein and set forth in the appended claims.

I claim: 1. Air refrigeration apparatus including: an air conducting conduit, an air propulsion means capable of circulating air through said conduit, an air cooling means located in said conduit having a first air inlet area, a second air inlet area and an air outlet area, said first inlet area being located in a plane normal to the direction of air flow through said conduit, said second air inlet area being located in a plane normal to said first inlet area, restriction means between said first and second air inlet areas, a plenum chamber lying between said restriction means and said second air inlet area, whereby in the absence of frosting conditions, the major volume of the air flows through said first inlet area and when, said first inlet becomes clogged with frost the restriction means permits a greater'volume of the air to flow through said second inlet area to said cooling element to thereby, provide for entry of air into said cooling element when the first inlet area becomes clogged with frost. 2. Air refrigerating apparatus as claimed in claim 1 having:

a frost collection cavity into which frost is propelled by an inertial force.

6 3. Air refrigeration apparatus as claimed in claim 1 5. Air refrigeration apparatus as claimed in claim 1 in which: including:

the cross section area of the air restriction means bea frost collecting cavity in said plenum chamber.

tween said first and said second air inlet areas is 6. Air refrigeration apparatus as claimed in claim 5 less than Va the cross section area of said first air 5 in which: inlet area. said restriction means is located at one end of said 4. Air refrigeration apparatus as claimed in claim 1 plenum chamber, in which: said frost collecting cavity is located in the other end said restriction means between said first and said secof said plenum chamber and,

0nd air inlet areas lies in a plane parallel to the 10 said second inlet area is located between said restricplane of said first inlet and normal to the plane of tion means and said frost collecting cavity.

said second inlet area. 

1. Air refrigeration apparatus including: an air conducting conduit, an air propulsion means capable of circulating air through said conduit, an air cooling means located in said conduit having a first air inlet area, a second air inlet area and an air outlet area, said first inlet area being located in a plane normal to the direction of air flow through said conduit, said second air inlet area being located in a plane normal to said first inlet area, restriction means between said first and second air inlet areas, a plenum chamber lying between said restriction means and said second air inlet area, whereby in the absence of frosting conditions, the major volume of the air flows through said first inlet area and when, said first inlet becomes clogged with frost the restriction means permits a greater volume of the air to flow through said second inlet area to said cooling element to thereby, provide for entry of air into said cooling element when the first inlet area becomes clogged with frost.
 2. Air refrigerating apparatus as claimed in claim 1 having: a frost collection cavity into which frost is propelled by an inertial force.
 3. Air refrigeration apparatus as claimed in claim 1 in which: the cross section area of the air restriction means between said first and said second air inlet areas is less than 1/3 the cross section area of said first air inlet area.
 4. Air refrigeration apparatus as claimed in claim 1 in which: said restriction means between said first and said second air inlet areas lies in a plane parallel to the plane of said first inlet and normal to the plane of said second inlet area.
 5. Air refrigeration apparatus as claimed in claim 1 including: a frost collecting cavity in said plenum chamber.
 6. Air refrigeration apparatus as claimed in claim 5 in which: said restriction means is located at one end of said plenum chamber, said frost collecting cavity is located in the other end of said plenum chamber and, said second inlet area is located between said restriction means and said frost collecting cavity. 